Carburetor choke mechanism



Feb. 3, 1959 F. w. HAMILTON CARBURETOR- CHOKE MECHANISM Filed Oct. 20,1955 2 sheets-sheet 1 Feb. 3, 1959 F. w. HAMILTON CARBURETOR cHoxEMECHANISM 2 Sheets-Sheet 2 Filed om.l 2o. 1955 a al l carburetorV body.

atfa convenient location and it is heated as it passes= United StatesPatent 40 y 2,871,843 y cannunnron oHoKE MECHANISM Francis W. Hamilton,Detroit, Mich., assigner' to Chrysler 'Cor-poration, Highland Park,Mich., a corporation of Delaware Applicationctober 20, 1955, Serial No.541,752 12 Claims. `(Cl. 123-119) M y present invention is generallybelieved related to liquid fuel carburetors for use with internalcombustion engmes. More particularly, my invention comprises a new andimproved carburetor choke mechanism which 1s possessed of improvedoperating characteristics.

This application comprises a continuation-in-part of my copendingapplication Serial No; 478,677, led December 30, 1954 and now abandoned.Y

The choke mechanism of my present invention is capable of beingsuccessfully employed in combination with a large variety of carburetormechanisms of known construction. However, for the purpose ofparticularly describing one structural environment for my invention, 1have presently disclosed a dual barrel carburetor which 1s especiallyadapted to be used with an internal com b ustlon gasoline engine of theautomotive type. This .carburetor structure comprises a cast bodyportion in which are formed a pair of downdraft fuel mixing condultswith` a choke valve situated on the upstream side thereof, saidconduitsy Vcommunicating with the engine mtakemanifold. During operationthe chokevalve may be caused to close the mixing conduit entrance duringenglne starting and engine warmup operation to increase the staticpressure drop the carburetor throat which 1n turn results in an enrichedfuel mixture. To provide for automatic operation of the choke valve, anengine temperature responsive thermostatic element is often provided foropening and closing the same; and to produce suicient breathing capacityduring idling operation when the engine is cold, an automatic unloadermechanism is often provided to crack open the choke -valve under theseconditions, said mechanism being inoperative to control the position ofthe choke valve when the engine reaches its normal operatingtemperature. Further, a suitable fast-idle mechanism is normallyemployed to crack open the throttle valves during idling operation whenthe engine is cold and when the choke valve is near its fully closedposition.

The choke valve is usually of the odset type so that the air forcesacting thereon as the air enters the mouth of the mixing conduits tendto open the choke valve while the thermostatic element opposes such anopening movement and urges the choke valve toward a closed positionduring engine starting and warmup.

In carburetors having such automatic chokes it has been common practiceto mount the vabove-mentioned thermostatic choke-control element on theupper portion of the carburetor casting substantially in alignment withthe shaft on which the choke valve is secured. To provide thethermostatic element of` such a choke control element with an enginetemperature signal, a hot air con duit or heater tube is interposedbetween the engine exhaust manifold and the region surrounding thethermostatic element, said region communicating with engine intakemanifold through passage means formed in the Air is caused to enter theheater tube 2,871,843 patented Feb. 3, 1959 ice 2 through that portionof the heater tube which traverses the exhaust manifold conduit. p

When the vehicle engine operates at or near widefopen 'throttle atrelatively low speeds, the engine intake mani- Aof time, the rate atwhich heated air is conducted into the region of the thermostaticelement is insucient to enable the choke control to maintain the chokevalve in the open position. Consequently, ythe choke valve is rotated inthese instances toward a closed position and the lfuel-air mixture ratiois thereby enriched until the mixture is no longer readily combustiblethus stalling or flooding the engine.

The choke valves of such conventional carburetors are normally coupledto the thermostatic element in Vsuch 'a way that the choke closingeffort of the thermostatic element is substantially the same regardlessof the angular position of the choke valve. If means are provided foradjusting the choke closing effort at an optimum value during enginestarting and warm-up, the choke closing effort during warm engineoperation would be too great. Conversely, if the choke closing` effortduring warm engine operation is fixed at an optimum value, the chokeclosing effort during starting `and warm-up would be insuicient topermit satisfactory engine operation under these latter conditions.Consequently, it has been the practice to strike a compromise and adjustthe device so that the closing eifort is atan optimum value only at someintermediatejchoke position between the two extremes. As a result, thechoke characteristics at any other choke position leaves much tobedesired.

The improved automatic choke assembly of my instant invention is freeofthe above-described shortcomings of the automotive chokes of knownconstruction and in addition it is characterized by certain otheradvantages which result in improved overall carburetor performance as Iwill subsequently point out.

The provision of an improved carburetor of the type mentioned abovebeing a principal object of my invention, it is a further object of myinvention to provide an automatic choke mechanism -for a liquid fuelcarburetor which is simple in construction, which is reliable inoperation and which may be readily installed on conventional gasolineengines.V

It is a vfurther object of my invention to provide an automatic chokemechanismy for a liquid fuel carburetor which includes a choke valveelement and a thermostatic control element for actuating the choke valveelement, said thermostatic control element being strategically situatedso that it is adapted to sense the choking requirements of the fuel andair mixing elements of the carburetor.

Another object of my invention is to provide an automatic chokemechanism for a liquid fuel carburetor which is characterized by aninherent delay in the opening ofthe choke valve element during theengine warmup period.

Another object of my invention is to provide an automatic chokemechanism for a liquid fuel carburetor which'is characterized by aninherent delay in the closing of the choke valve element while theengine is cooling down.

Another object of my invention is to provide an automatic carburetorchoke mechanism which includes a choke valve-element and a means forsupplying a variable choke valve closing' eiiort` thereto, the magnitudeof the choke valve closing eiortvbeing greater when the choke valveapproaches a closed position than when it approaches an open position.

It is a further object of my invention to provide a new and improvedautomatic choke device which is possessed of a new and improvedoperating characteristic.

In carrying forth the foregoing objects, I have provided a downdraftcarburetor with a choke valve element disposed within the downdraftconduit means thereof and with a novel linkage mechanism for rotatablyactuating the choke valve element to restrict the flow of carburetorintake air during those instances when choking is desired. A pocket maybe formed in the engine exhaust gas crossover section of the intakemanifold structure and a thermostatic control element may be suitablymounted therein. The above-mentioned linkage mechanism may extend to theinterior of the intake manifold pocket and may be operatively connectedto the thermostatic control element for varying the choke valve settingin response to variations in engine operating temperature. The manifoldpocket is positioned in the exhaust gas crossover passage adjacent thefuel mixing downdraft conduits of the carburetor and is subjected to theheated exhaust gases during operation of the engine.

The temperature to which the thermostatic control element may be heatedis independent of engine intake manifold vacuum pressure and is afunction only of the engine operating temperature. The strategiclocation of the thermostatic control element, as above described,enables the same to respond to variations in operating temperature inthe proximate vicinity of the carburetor fuel mixing conduits and toprovide the proper degree of choking for any operating temperature.

The above-mentioned linkage mechanism comprises one of the principalfeatures of my instant invention and it is comprised of linkage elementswhich are capable of adjusting the effective leverage between the chokevalve shaft and the thermostatic element as the latter expands 'orcontracts due to variations in engine operating temperature.

For the purpose of more particularly describing the novel features of myinstant invention, reference will n be made in the following descriptionto the accompanying drawings wherein:

Figure 1 shows a transverse cross sectional view of a dual downcraftcarburetor for use with an automotivev type gasoline engine;

Figure 2 is a plan View of portions of the manifold system for theabove-mentioned gasoline engine and it shows the manifold crossoverpassage upon which the carburetor of Figure l may be mounted;

Figure 3 is a side view of the carburetor of Figure l showing in sectionthe manifold pocket within which the thermostatic control element ismounted and is taken along section line 3 3 of Figure l;

Figure 4 is a side view of the other side of the carburetor of Figure lshowing a portion of the throttle valve linkage mechanism and the chokevalve linkage mechanism;

Figure 5 is a detail sectional view of the thermostatic control elementshown in Figures l and 3 and is taken along section line 5 5 of Figure3;

Figure 6 is another sectional view of the thermostatic control elementshown in Figure 5 and is taken along section line 6 6 of Figure 5; and

Figure 7 is a graph showing the operating characteristics of the chokemechanism of Figures l through 6.

Referring first to Figure l, the carburetor body in cludes threeprincipal portions which are separately identitied by numerals it), 12,and 14, the portion 1t) being hereinafter referred to as the uppercarburetor body portion, the body portion 12 being referred to as theintermediate carburetor body portion and the portion 14 beinghereinafter referred to as the lower body portion. The lower bodyportion 14 is provided with a pair of mixture conduits identified bynumerals 16 and 18 and it is secured to an upper surface 20 of a castconduit portion of the engine intake manifold system, the latter beinggenerally designated by numeral 22. A suitable gasket 24 may beinterposed between the mating surfaces of the lower carburetor bodyportion 14 and the intake manifold portion 22. A pair of throttle valves26 and 28 are rotatably mounted within the mixture conduits 16 and 18respectively, and they are secured to a common throttle shaft 30 whichis transversely disposed within the conduits 16 and 18 and rotatablyjournalled in the carburetor body portion 14.

One end of the throttle shaft 30 carries a throttle linkage element 32which may form a portion of a manually operable throttle linkagemechanism. The other end of the throttle shaft 30 has secured thereto atransversely extending element 34, a screw 36 being provided for thispurpose. As best seen in Figure 4, an adjustable stop element 38 isthreadably received through a threaded aperture in the element 34.

The intermediate carburetor body portion 12 comprises a pair of throatsor venturi passages 40 and 42 which are respectively aligned withmixture conduits 16 and 18 of the carburetor body portion 14. Thethroats 40 and 42 communicate at the upper ends thereof with a commonintake air passage 44 which is defined by the outermost wall structureof the carburetor body portion 12. A pair of small venturi elements 46and 48 are positioned directly above each of the throats 40 and 42respectively. These venturi elements 46 and 48 are integrally joined toa centrally disposed fuel metering mechanism, the exterior of which isshown at 50. The

lindividual small venturi elements 46 and 48 are joined to the meteringmechanism 50 by means of integral extensions 52 and 54. This meteringmechanism is adapted to supply fuel nozzles, one of which extends intoeach of the small venturi elements 46 and 48, with a controlled supplyof, liquid fuel which is mixed with the intake air passing through theventuri sections of each of the elements 46 and 48.

The lower surface of the intermediate carburetor portion 12 is securedto the upper surface of the lower carburetor body 14 and a suitablegasket 56 is interposed therebetween as shown.

A vacuum idle unloader cylinder 58 may be formed vertically within anintegral extension 60 of the intermediate housing portion 12 and thelower portion thereof may be provided with a plurality of axiallyextending grooves 62. The interiorof the cylinder 58 communicates withthe mixture conduit 16 below the throttle valve element 26 throughcommunicating passages 64 and 66 formed in the carburetor body portions12 and 14 respectively.

A fulcrum element 68 may be formed on theside of the extension 60 and,as best seen in Figure 4, a cam element 70 may be journalled thereon.The cam element 70 may be secured in position by a suitable screw 72with an extension 74 thereof being free to oscillate substantially inthe plane of the above-described throttle element 34. The cam extension74 is provided with a camming surface 76 which is adapted to Contact theadjustable throttle element 38 when the throttle valves assume a closedposition as shown in Figure l.

The upper carburetor portion 10 denes a single carburetor intake airpassage 78 which communicates with the above-described air passage 44`and the intermediate carburetor body portion 12. A carburetor chokevalve element 8i) is positioned within the intake conduit 78 and issecured to a rotatable choke valve shaft 82, the latter beingtransversely disposed in the air conduit 78 and rotatably journalled ateither end thereof in the walls of thc carburetor cast body portion 10.One end of the choke valve shaft 82 has secured thereto a linkageelement 84, as best seen in Figure 4, said linkage element 84 beingadapted to rotate with the choke valve shaft 82 as the latter isactuated. A vacuum idle unloader piston element 86 is slidably `receivedwithinthe above-described cylinder 5,8. and is operatively joinedtotherlink element 84, by meansot' another linkelemert. Itis thus seenthat as :the ,piston element 8,6 moves in a downward rdirection withinthe cylinder 58 the choke valve element 80` is .caused to rotate, towardan-open-position. Thepiston 86 `is caused to move in response ,tovariations-in intake manifold pressure since the portion of the cylinder58 below 4the piston 86 is in communication with the .intakermanifoldthrough the .passages `6.4a11d `66, as above explained. The piston.element :86 .isprovided with a transversely extending -passage V90which is ,adapted to communicate with the above-mentioned longitudinalgrooves62 formed in the` cylinder 58 when the piston 86 moves apredetermineddistance in a downward direction as viewed in Fig- .ure 1.When the passage 90 `and the groove 62 are in communication, furtherdownward movement of the piston 86 in response to intake manifold vacuumpressure variations is prevented.

As illustrated in Figure 1, the cylinder 58 may communicate with theatmosphere thereby permitting atmospheric air to be drawn through thepassages 64 and 66. However, it is often preferable to form the cylinderso `that it communicates with the interior of the air passage 78 on theupstream side of' the choke valve element 8i) rather than directly withthe atmosphere. Since aconventional air cleaner, not shown, is normallysituated on the upstream side of the air intake `passage 78, the airwhich would be delivered to the Cylinder S8 in the latter case wouldnecessarily be relatively clean air that is free of foreign matter.

Another portion of thelinkage element 84-may beoperatively connected tothe above-described cam element 7i) by means of a linkage element 92.Itis thusseen that as they choke valve element 8,0 is moved towardva'fully closed position, the cam element 70 will be caused to contactthe adjustable element 38 Vcarried by the throttle linkage element 34thereby causing the throttle valves 26 and28to be cracked open toprovide a fast idle. A

lost motion slot connection between 'linkage elements` 92 and 84 isprovided at 93 to Vpermit the choke valve 80 yto open independently ofthecam element'7tiand the throttle `valves. As b'est seen in lFigure 1j,a coil spring 9Smay -b e provided about fulcrum 68 to normally bias camelement 70 in a counterclockwise direction as viewed in Figure 4. g

The three carburetor cast body portions 10, 12, and 1 4 may be securedtogether by means of "bolts 94, as best seen in Figures 3 and 4, to forman integral assembly. A conventional air cleaner device may be securedto the ltop of the carburetor body portion 1i) if desired although sucha device is not illustrated in the drawings. The intermediate carburetorbody portion 12 further includes a fuel bowl -96 having a` fuelinletfitting 98 as best'seen `in Figures 3 and 4. A portion of anaccelerator pumping mechanism may be seen inFigures 3 and4 at 160, and aconventional idle adjusting element 101 may also be provided inthe lowercarburetor body portion 14.

Referring next to Figure`2, a portion of the intake manifold system fora typical V-S K gasoline engine is shown and it comprises a plurality ofintake conduits individually shown at 102, 164, 106', 108, 11d, 114,116, and ll'which are Vadapted to deliver a combustible mixture to eachof the eight cylinders of the engine. The conduits V102 and 114Vcommunicate with a single conduit portion 120, and the conduits 108 and116 communicate with a single conduitportion 122. The conduit portions120 and 122 in turn ycommunicate with a vertically vextending passage124` which forms a continuation of the carburetor mixture conduit 18,said Ipassage 124 being below the conduits 108 and 116, `as viewed inFigure ,'24, and they communicate with a common conduit portion 130.Conduit portionsl 128 and 130 in turn communi- Cate with a verticallyextending passage 132 formed in `the carburetor mounting iange 126. Thepassage 1 32 is adapted to communicate with and form an extension of theabove-described. mixture conduit 16. For the purpose of clarity, thepassage of combustible mixture through each of the above-describedintake manifold conduits is represented by arrows, the arrowsrepresenting the iiow of mixture throughconduits 102, 108, 114, and 116being dened by dash and dot lines and the arrows -representing the ilowof the mixture through conduits 104, 106, ,110., and 118'being definedby dotted lines.

' The above-describedmixture passages 124 and 132 are defined in part byintake risers generally designated vby the numerals `134 and 13.6respectively, said risers being integrally formed with the carburetormounting `ange and the intake Iconduit structure as part of anintegrally cast assembly. The intake riser 134 communicates with `theconduit portions 120 and 122 at the lower end thereof and the intakeriser 136 communicates with the conduit portions 128 and 130at its lowerportion. Since the con- `duit portions 128 and 130 must necessarily beformed below the conduit portions 120 and 122 as above explained, theintake riser 13 6 is formed deeper than the intake riser 134, this beingapparent from the cross sectional view ofFigure ,1.

An eight cylinder engine of this type isnormally formed with an exhaustmanifold conduit on either side of the engine, the four cylinders on oneside of theengine comrnunicatingV with one exhaust manifold conduit andthe four cyinders `on the other side of the engine communicating withthe otherexhaustmanifold conduit. An exhaust gas crossover passage isnormally provided for interconnecting the above-mentioned exhaustmanifold conduits to accommodate the flow of exhaust gases therebetween.This exhaust gas crossover passage is identified in Figures l and 2 bynumeral 138 and it forms a portion of the integrally cast intakemanifold structure.

Crossover passage 138 Vincludes a central portion which formed in acarburetor mounting flange identified in I surroundsthe above-describedintake manifold` risers. For the purpose of clarity, the flow of exhaustgases from one side of the crossover passage 13S to the other isrepresented by means of arrows and it is apparent that the intakeVrisers are engulfed by the hot exhaust gases throughout their entirelength. The combustible mixture is thereby heated by the exhaust gasesduring operation, and in order to provide substantially equal heatdistribution between each of the intake risers 134 and 136, a bafe 140Vis formedintegrally on the bottom of the intake riser 134, said baffle140 being effective to direct the iiow of exhaust gases around thebottom of the intake riser 136 as shown.

As best seen in Figures 1 and 3, I have formed a well 142 in the upperwall of the exhaust gas crossover passage 138 audit extends downwardlyinto `the path of the exhaust gases as they pass from` one side ofthecrossover passage 138 to the other. I have positioned a thermostaticcontrol element 144 within the well 142` and have enclosed the well 142by a cover plate 146 which maybe secured in place by suitable screws orthe like. A linkage element 148 is operatively connected to thethermostatic c-ontrolelement 144 at one end thereof and it extendsvertically upward through an aperture 1,50 yformed inthe cover plate146. A suitable dust cap or washer 152 may be provided as shown, ifdesired, to ,prevent the entry of foreign matter into the well 142through the aperture 15G. The -other end of the linkage element 148 issecured to one end of a choke linkage `element 15,4 as bestV seen inFigure 3, the linkage element 154 being operatively joined to the chokevalve shaft 82. The. thermostatic control element 144 is` adapted toallow the linkageA element 148 to move in a downwardly `direction, asviewed in Figure l, as the temperature of the '138. It will be apparentfrom Figures 1 and 3 that this downward movement of the linkage element148 will be accompanied by movement of the choke valve element 80 towardan open position. This choke valve is adapted to move toward an openposition by virtue of the offset location of the choke valve shaft 82.

Referring next to Figures and 6, the thermostatic control element 144 isshown in more particular detail and it includes a bracket 156 extendingin a downward direction within the well 142 and is secured at the upperendthereof to the upper surface 158 of the Well 142. The top side of thebracket 156 extends about the periphery of the well 142 and is securedin place by the bolts which retain the cover plate 146 in place. A coilanchor post is shown at 160 and is received within an aperture formed inthe lower portion of the bracket 156 and secured therein by a nut 162.An adjustable plate 164 is interposed between the base of the anchorpost 160 and the supporting bracket 156, said plate being nonrotatablewith respect to the anchor post 160.

As best seen in Figure 3, the plate 164 may be marked with an indicatormarking 166 and the lower portion of the bracket 156 may be providedwith a series of grada- 'of the anchor pin 160 as shown at 172, toprevent axial movement of the shell 170 with respect to the anchor 'pin160. f

The above-mentioned linkage element 148 is formed at the lower endthereof with a transversely extending portion 174 which may be receivedthrough aligned apertures in the end walls of the circular shell 170,said extension f 174 terminating on the exterior of the shell 170. Asuitable locking device 176 may be carried by the terminal end of thelinkage element extension 174.

As best seen in Figures 5 and 6, a thermostatic coil element 178 ispositioned within the shell 170 and the inner end of the coil isreceived within a slot 188 formed in the anchor pin 166. The radiallyoutward end of the coil 178 encircles the linkage element extension 174thereby enabling the coil 178 to impart a turning eiort to the shell 170when the coil 178 becomes stressed. As the shell 170 is caused to rotatein a. clockwise direction, as viewed in Figure 6, Ian upward force willbe imparted to the linkage element 148 thereby causing the choke valveelement S0 to move toward a closed position.

In operation, a combustible fuel and air mixture is caused to passthrough the mixture conduits 16 and 18 into the intake risers 134 and136 which in turn supply each of the individual intake manifold conduitsshown in Figure 2. The throttle valves 26 and 23 control the rate ofilow of combustible mixtures to the intake risers in the conventionalmanner. When the engine is cold `the thermostatic element 178 iseffective to allow the shell 170 to move in a clockwise direction, asviewed in Figure 6, thereby allowing the choke valve element 80 toassume a closed position. As the exhaust gases continue to pass throughthe exhaust crossover passage 138 during the warm up period of theengine, the thermostatic element 178 becomes heated which causes theouter end of the thermostatic element 178 to move in a counterclockwisedirection about the anchor post 16h. This in turn allows the shell 170to pivot about yanchor post 160 in a counterclockwise direction therebyallowing the choke valve element Sil to move to an open position. Itwill be apparent that the position of the choke valve elementisdetermined solely by the tcmperature to which the thermostatic element178 becomes heated and except for the operation of the choke unloadermechanism, it is in no way influenced by variations in engine intakemanifold pressure as in the automatic choke mechanisms of knownconstruction.

During idling operation when the engine is cold, the intake manifoldvacuum pressure will be suicient to cause the vacuum motor unloaderpiston to be depressed within the cylinder 58 until the transversepassage 90 in the piston element 86 communicates with the cylindergrooves 62. This is accompanied by a slight opening movement of thechoke valve 80 as previously indicated. This movement of the pistonelement 86 will also cause the cam element 70 to rotate in a clockwisedirection, as viewed in Figure 4, and will cause the throttle valveelements 26 and 28 to assume a fast idle position as previouslyexplained.

The thermostatic control element 144 may be conveniently disassembledmerely by removing the screws which secure the cover plate 146 to thecrossover passage 138. An adjustment in the initial setting of thethermostatic control element may be conveniently made by loosening thenut 162 `and by adjustably positioning the plate 164 with respect to thesupporting bracket 156, and the extent of the adjustment may be measuredby means of the graduated markings 168 as shown in Figure 3. angularmovement of the adjustable plate 162 is accompanied by movement of theanchor pin which in turn tends to either wind or unwind the coils of thethermostatic element 178 depending upon the direction of rotation of theplate 162. This in turn varies the linitial tension of the windings forthe thermostatic element.

The above-described choke construction will provide Va desirable delayin the opening of the choke valve element during the warm up period thusassuring that the fuel and air mixture will be sufficiently rich tomaintain steady and smooth engine operation until the engine operatingtemperature becomes stabilized at its normal operating value. i

Similarly, the choke construction of my instant inventionprovides aninherent delay in the closing of the choke valve while the engine iscooling. This feature prevents an over-rich mixture from being suppliedto the engine intake manifold when the engine is started before it hascooled down to the temperature of the ambient air. The shell 170`functions to provide an added heat darn which is capable of storingthermal energy to accentuate the above-described time delay feature.

Because of the strategic location of the thermostatic control mechanismof the choke of my instant invention, the choke valve 80 respondsdirectly to variations in the temperature signal existing in theproximate vicinity of the fuel mixing conduits and is sensitive to theactual engine choking requirements whereas the automatic chokemechanisms of known construction employ some other temperature as anoperating signal. These con ventional mechanisms `are therefore notdirectly sensitive to the engine choking requirements.

With choke mechanisms of known construction, prcviously described, theproblem of obtaining clean air for heating the thermostatic elementoffers considerable difculty. With the choke construction of my instantinvention, this problem is completely eliminated since no air is drawnthrough the thermostatic element. Also the choke operating air of theconventional choke devices bypasses the throttle and this bypassed airmakes it extremely difficult to obtain proper engine idling operation.This problem is greatly aggravated when four barrel carburetors ratherthan single or dual barrel carburetors are employed since secondarythrottle valve leakage as well as primary throttle valve leakage mustthen be considered. The carburetor choke of my instant invention,however, completely eliminates the bypassing of air around the throttlethrough the thermostatic element.

This.

It will be apparent from 'Figures 3, 5, and 6` that the linkage element154 assumes a substantially' horizontal position when the choke valveelement 80 is in a closed position. Further, the connection between the.linkage element 148 and the rotatable shell 170 approaches a top deadcenter position when the choke valve element approaches a closedposition, and the angle formed by the linkage element 14S and a radialline connecting the axis of rotation of the shell V170 and the point ofconnection between the shell 170 and the linkage element 148 form anangle which is only slightly less than 180. By way of contrast it maybeobserved that the linkage element 154 assumes a downwardly extendingposition, as shown in Figure, 3, when the choke valve element'approaches a Wide vopen position. Also, the radial line connecting theaxis ofthe shell 170 with the point of connection between the shell 170and the linkage element `148 assumes a substantially horizontal`position andY thel angle formed `by this line and the linkagetelement148 is substantially a right angle. It is thus seen that theclosingtorque applied tothe choke valve element 8i) by reason of thetension of the thermostatic coil spring 178y willbe atVa'maximum'whenthe choke valve element assumes a `closed position andwill berat a minimum when it assumes an open position. In other words,the Y ratio ofthe length of the leverage arm between the axis of thethrottle valve shaft 82 and the working axis of thelinkage element A1,48to the length of theleverage arm between the axis ofthe shell 170 andthe working axis of the linkage element 148 will become progressivelygreater as the choke valve approaches a closed position. As this ratioincreases, the closing effort will be correspondingly increased for agiven lspring tension in the thermostatic coil element V178. i V

"For the lpurpose of graphically illustrating the effect of -theimproved choke construction of my instant invention upon the carburetorperformance, a briefre'ference will be made to Figure 7 wherein the`fuel air ratio for a -typical automotive type engine is plotted as anordinate Iwiththe air iiow rate as an abscissa. During engine crankingit is desirable to provide a rich fuel mixture and this operatingcondition is represented on the performance chart by point A. Aslcombustion is initiated, the fuel air ratio will rapidly decrease andthe variation of the fuell air ratio with Vrespect'to the air flow ratedurvingthis transient operating condition may be represented -by a curvehaving a large negative slope.

For purposes of illustration, curve 1in the` chart of Figure 7represents the variation of fuel air ratio with air flow which would beobtained with a conventional Vtype carburetor in which the choke valveclosing torque remains substantially constant at all operating4positions of the choke. lf it is assumed that the optimum closingtorque for such `a conventional carburetor occurs when the choke valveis partially open thereby providing an optimum fuel mixture ratio duringwarm-up, thevmagnitude of the fuel air ratio will be too low to maintaincombustion during co-ld starting and the engine will lstall immediatelyafter combustion is initiated. Acceleration of the engine up to thenormal `operating speed is impossible under these conditions, thevariation in fuel-air ratio rapidly diminishing as illustrated by curve1.

The minimum fuel air ratios for various air iiow rates which arerequired in order to maintain combustion are represented in the chart ofFigure 7 by curve 3', and any fuel air ratio fora given air flow rateshould be above curve 3 if the engine is to operatesatisfactorily/without stalling. It is apparent from the chart ofFigure7 that a portion of `curve 1 falls considerably below theoperating limit, as represented by curve 3, and therefore'the enginewill stall as the air flow rate is increased upon acceleration of theengine since the fuel mixture will be too lean. If the tension of thethermostatic coil element is increased so that the effort applied to thechoke valve will be greater Vthroughout the entire choke angulartravel,k the upper portion of `the performance curve 1 will be raisedtoa considerably richer fuel a'ir ratio and the lower portion of the curve will fall outside the operatingV limit repre,- sented by curve 3.However, under such circumstances itis highly probable that the fuel airmixture will betoo rich at the higher air flow rates as the engine isaccelera ated during the warmup period or as the engine is throttledback to` anidling speed with the vacuum actuated choke unloadermechanism energized. Such a modied curve hasnotbeen represented inFigure 7 but it would be similar in shape to curve A1 except that itwould be shifted a substantial distance in a vertical direction.

1f Ya compromise between the two above-described conditions ismade, theoptimurnperformance of the engine when the choke valve is near theclosed position and when it is in a partially open position will besacrificed in order to permit the engine to operate throughout theentire'speedyrange. By way of contrast with the above, the variablelleverage controlledjlinkage mechanism of thechoke of my. invention iscapable of applying a relatively highclosing torque tothe choke valvewhen the operating point is in the region of point A and a low `closingtorque to the choke valve when 4the operating point is in the higher airow region. The variationin fuel air ratio with various air flow rateswhich is obtained with a carburetor employing the improved chokemechanism of my instant invention is represented in Figure 7 by curve 2.It may be observed that all of curve 2 'is situated above theoperatinglimit of curve 3.

Aimpossible for the operating point to move along curve 1 'from point Ato the point of intersection of curve 1 with curve 4 unless the. engineis accelerated by means of a push start or unless power is deliveredtothe enginefrom an externalpower source.

What I claim and .desire to secure by United States Letters Patent is:

1., 'In a liquid fuel carburetor for an internal'combustion enginehaving' a plurality of cylinders, intake mani fold conduits forconducting a combustible fuel and air mixture to said cylinders, anexhaust manifold including portions disposed near opposite sides of saidengine, an exhaust gas crossover passage `interconnecting said exhaustmanifold portions, an intake manifold riser forming a portion of saidintake manifold conduits, said in take riser being disposed within `saidexhaust gas crossover passage; at least one downdraft mixture conduitformed within said carburetor, said carburetor being secured to saidintake manifold with said intake riser communicating with said mixtureconduit, a throttle valve element disposed within said -mixture conduitfor controlling the ow of combustible fuel mixture therethrough, saidmixture conduit communicating with a carburetor air intake passage, achoke valve elementdis.- posed' within said intake passage, a wellformed in said crossover passage, a thermostatic control elementdisposed in said well, and linkage means interconnecting saidthermostatic control element and said choke valve for adjustiablypositioning the latter inresponse to variations in engine operatingtemperature.

2. In a liquid fuel carburetor for use with an internal combustionengine having a plurality of cylinders, intake manifold conduitsforconducting a combustible fuel and air mixture to said cylinders, anexhaust manifold including portions disposed near opposite sides of saidengine, an exhaustgas crossover passage interconnecting said exhaustmanifold portions, an intake manifold riser forming a portion of saidintake manifold conduit` said intake riser `being disposed within saidexhaust gas crossover passage; at least one downdraft mixture conduitformed within said carburetor, said carburetor being secured to saidintake manifold with said intake riser communicating with said mixtureconduit, throttle valve elements disposed within said mixture conduitfor controlling the flow of combustible fuel mixture therethrough, saidmixture conduit communicating with a carburetor air intake passage, achoke valve element disposed within said intake passage, a well formedin said crossover passage, a thermostatic control element disposed insaid well, said thermostatic control element including a helicalbi-metallic coil, means for anchoring the inner end of said coil in astationary position, and a linkage means including a portion mountedadjacent said coil, the other end of said coil being operativelyconnected to said portion of said linkage means, said linkage meansbeing operatively connected to said choke valve element for adjustablypositioning the same in response to variations in the temperatureexisting within said well.

3. In a liquid fuel carburetor for use with an internal combustionengine having a plurality of cylinders, intake manifold conduits forconducting a combustible fuel and air mixture to said cylinders, anexhaust manifold including portions disposed near opposite sides of saidengine, an exhaust gas crossover passage interconnecting said exhaustmanifold portions, an intake manifold riser forming a portion of saidintake manifold conduits, said intake riser being disposed Within saidexhaust gas crossover passage; at least one downdraft mixture conduitformed within said carburetor, said carburetor being secured to saidintake manifold with said intake riser communicating with said mixtureconduit, throttle valve elements disposed within said mixture conduitfor controlling the flow of combustible fuel mixture therethrough, saidmixture conduit communicating with a carburetor air intake passage, achoke valve element disposed within said intake passage, a well formedin said crossover passage, said thermostatic control element including abi-metallic helical coil, an anchor pin, one end of said coil beingsecured to said anchor pin, means for supporting said -anchor pin withinsaid well, linkage means interconnecting said choke valve element andthe other end of said coil, said anchor pin being movable to any of aplurality of fixed angular positions to vary the initial tension of`said coil.

4. The combination as set forth in claim 3 wherein said means forsupporting said anchor pin includes a plate member extending into saidwell, said anchor pin being rotatably secured to said plate member, andan indicator element secured to said anchor pin adjacent said platemember, said indicator element being movable with said anchor pinthereby providing an indication of the angular position of said anchorpin.

5. In a liquid fuel carburetor for use with an internal combustionengine, said engine including an intake manifold and an exhaust gasmanifold; at least one downdraft carburetor mixture conduit, an airintake passage cornmunicating with said mixture conduit, a choke valveelement movably mounted in said air intake passage for providing acontrolled restriction to the flow of intake air through said intake airpassage, an exhaust gas crossover passage formed in the vicinity of saidintake manifold and interconnecting portions of said exhaust gasmanifold, a well formed in said crossover passage, said well defining apocket which is adapted to ybe surrounded by engine exhaust gases duringoperation of the engine, a thermostatic control element disposed in saidpocket, and a linkage means operatively connected to said choke valveand extending therefrom into said pocket, said thermostatic controlelement including a portion operatively connected to said linkage means,said choke valve being movable into and out of an intake air passageclosing position in response to variations in the temperature existingwithin said pocket.

6. ln a-liquid fuel carburetor for use with an internal combustionengine, said engine including an intake manifold and an exhaust gasmanifold; at least one downdraft carburetor mixture conduit, an airintake passage communicating with said mixture conduit, said carburetorbeing mounted upon said intake manifold with said mixture conduitcommunicating with said intake passage, a choke valve element movablymounted in said air intake passage for providing a controlledrestriction to the flow of intake air through said intake passage, athrottle valve means including a throttle valve element movably mountedin said mixture conduit for controlling the flow of combustible .fueland air mixture therethrough, an exhaust gas crossover passage formed inthe vicinity of said intake manifold and interconnecting portions ofsaid exhaust gas manifold, a Well formed in said crossover passage, saidwell defining a pocket which is adapted to be surrounded by engineexhaust gases during operation of the engine, a thermostatic controlelement disposed in said pocket, a linkage means operatively connectedto said choke valve and extending therefrom into said pocket, saidthermostatic control element including a portion operatively connectedto said linkage means, said choke valve element being movable into andout of an intake air passage closing position in response to variationsin the temperature existing within said pocket, a cam element rotatablymounted on a portion of said carburetor, other linkage means operativelyconnecting said choke valve and said cam element, said cam element beingadapted to contact a portion of said throttle valve means and to crackopen said throttle valve element to provide a fast idle when said chokevalve approaches a fully closed position, and means for cracking opensaid bracket means is removably attached to a portion of said crossoverpassage and wherein said anchor element may be rotatably adjusted to apreselected position to vary the initial tension of said helical coilasdesired.

9. In a liquid fuel carburetor for use with an internal combustionengine, said engine including an intake manifold and an exhaust gasmanifold, at least one downdraft carburetor mixture conduit, an airintake passage, said carburetor being mounted upon said intake manifoldwith said mixture conduit communicating Vwith said intake passage, achoke valve element movably mounted in said air intake passage forproviding a controlled restriction to the flow of intake air throughsaid intake air passage, an exhaust gas crossover passage in theimmediate vicinity of a portion of said intake manifold andinterconnecting portions of said exhaust gas manifold, a well formed insaid crossover passage, said well defining a pocket which is adapted tobe surrounded by engine exhaust gases during operation of the engine, athermostatic control element disposed in said pocket, and linkage meansoperatively connected to said choke valve and extending therefrom tosaid thermostatic control element, vsaid thermostatic control elementincluding a helical, bi-metallic coil, an anchor element, a cover plateremovably secured over said pocket, a bracket means for supporting saidanchor element, the inner end of said helical coil being secured toVsaid anchor element, a member rotatably mounted on said anchor elementadjacent said helical coil, the other end of saidhelical coil beingoperatively connected to said member, said member forming a portion ofsaid linkage means and rotatable about said anchor element in responseto variations in the ambient temperature in the vicinity of said helicalcoil within said pocket.

10. In a liquid fuel carburetor for an internal combustion engine havinga plurality of cylinders, an intake manifold having con-duits forconducting a combustible fuel and air mixture to said cylindersanexhaust manifold including portions disposed on opposite sides of saidengine, an exhaust gas crossover passage interconnecting said exhaustmanifold portions, an intake manifold riser forming a portion of saidintake manifold conduits, said exhaust gas crossover passage at leastpartially surrounding said riser; at least one dovvndraft mixtureconduit formed Within said carburetor, said carburetor being secured tosaid intake manifold With said intake riser communicating with saidmixture conduit, a throttle valve element disposed within said mixtureconduit for controlling the ow of combustible fuel mixture therethrough,said mixture conduit communicating with a carburetor air intake passage,a choke valve element dispose within said intake passage, a well formedin said crossover passage in the proximate vicinity of said intakeriser, a thermostatic control element disposed in said well, and linkagemeans interconnecting said thermostatic control element and said chokevalve for adjustably positioning the latter, said thermostatic Controlelement responding to variations in the engine operating temperature inthe immediate vicinity of said intake manifold riser to effect anadjustment of said choke valve, the magnitude of said adjustment beingdirectly responsive to the engine choking requirements.

1l. In a liquid fuel carburetor for an internal combustion engine havingan intake manifold and an exhaust manifold, at least one downdraftmixture conduit communicating with said intake manifold withA a portionof the latter being defined by said mixture conduit, an air intakepassage communicating with said mixture conduit, a choke valve elementmovably mounted in said intake passage, an exhaust gas passage connectedto said exhaust manifold, a recess formed in said exhaust gas passage inclose proximity to said mixture conduit portion, a thermostatic controlelement disposed in said recess, and a linkage means operativelyconnecting said choke valve element With said thermostatic controlelement for .controlling the movement of the former in response toengine operating temperature.

12. In a liquid fuel carburetor for an internal combustion engine havingan intake manifold and anexhaust gas manifold, at least one fuel mixtureconduit communicating With a portion of the said intake manifold, an airintake passage formed on the upstream side of said mixture conduit, achoke valve element movably mounted in said air intake passage, anexhaust gas passage communicating with said exhaust gas manifold, arecess formed in said exhaust gas passage in the proximate vicinity ofsaid intake manifold portion, and a temperature responsive control meanssituated at least in part within said recess with a portion thereofbeing operatively connected to said choke valve element, said controlmeans being adapted to adjustably position said -choke valve element inresponse to the choking requirements.

References Cited in the tile of this patent UNITED STATES PATENTS2,152,078 Moore Mar. 28, 1939 2,222,865 Chandler Nov. 26, 1940 2,324,592Olson July 20, 1943 2,427,030 Swigert Sept. 9, 1947 2,702,536 CarlsonFeb. 22, 1955 2,705,484 Jorgensen et al. Apr. 5, 1955 Attesting OcerUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 871,843February 3, l959 'Francie Wo Hamilton It is hereby certified that errorap of the above numbered patent requiring co l Patent should read ascorrected below.

pears in the printed specification rrection and that the said LettersColumn 6;, line '74, for Hdownwardly" reed ==fdownward me# column lO,q

3 line 36, for "is would" reed me it would en; column 1 3'g line 18, for"dispose read e disposed ze column l49 line 8g for "temperature" reed e@temperature Signed and sealed this 2nd day of June 1959i7 (SEAL) Attest:

EARL E. AXLINE ROBERT C. WATSON Commissioner of Patents

